I agree that Publii is currently lacking full control for post order, but the truth is that every other major CMS that I’ve used also lacks this feature.
It’s obvious that most sites get by fine without this type of control, but I agree that it would be a very useful feature for certain projects.
You’re right that you can modify the publish date as a hack to get what you want. It will probably be best to disable “Display date” in your theme settings.
One thing to keep in mind is that even if you disable showing the display date in the theme settings, Publii will still publish the date as metadata. This means that as you manipulate the publish date to fit your ideal post ordering, a search engine algorithm might notice the date changes and think that you’re trying to manipulate the ranking system by changing the publish date of your content without actually changing the content. Who knows, but it is possible. I guess it doesn’t matter if you have no desire to reach readers through SEO.
You might consider not using your blog roll or tag archives at all and instead create all of your links by hand. If it’s a smaller site then this might be your best bet if you want full control over the order of your posts. Set your homepage to display a post instead of the blog roll and basically maintain your own blog roll by hand. You’ll give up most of what makes using a CMS so great, but you’ll have no problem controlling the order of your site’s content.
I’m not sure what a true solution to having full control over the order of your posts would look like, but if it was ever solved it would be one more reason for me to use Publii over other platforms.